reconsider use of ETag

Given that the ETag algorithm is well known and public at this point, would you reconsider using it? Yes, computing it depends upon knowing the chunk size, but you can use this fact when uploading to confirm that the data is written correctly. You could compute the Etag for any given multipart size while uploading (the md5sum of chunk md5sums) and store the chunk size with the object in custom metadata for retrieval purposes. At the very least, it would provide a very high standard for upload verification and data integrity guarantee.
https://stackoverflow.com/questions/12186993/what-is-the-algorithm-to-compute-the-amazon-s3-etag-for-a-file-larger-than-5gb

No files, tests, or entry points are named. Start by locating the multipart upload path and existing integrity or metadata handling, then clarify the intended ETag behavior, supported chunk sizes, and verification expectations before determining the relevant test coverage.

Written by the indexing model from the issue text.